The present invention relates to a method of protecting floors above the crawl space and buildings on foundations of the crawl-space type from damp and microbial growth, where the crawl space is delimited by the floor above the crawl space of the building, bearing foundation walls with vents for outdoor air and the foundation ground.
The invention also relates to an arrangement for use in application of the method.
Building foundations of the crawl-space type, that is to say foundations where there is a crawl space between the floor of the building and the foundation ground, which crawl space is delimited in the lateral direction by bearing foundation walls, have traditionally been ventilated with outdoor air via vents located in the foundation walls. Foundations of this type have functioned well in the past, one of the reasons for which is the fact that chimneys extended through the floor above the crawl space and down into the crawl space, which thus contributed to warming and drying the foundation and the air therein. A certain degree of heat leakage down into the crawl space from rooms above also took place as a consequence of poor insulation of the floor above the crawl space. This, combined with correctly effected ventilation, meant it was possible to avoid problems of damp and mildew.
As crawl-space foundations ventilated by outdoor air constitute a cost-effective foundation method, this method was used during the second half of the twentieth century in the mass production of dwelling houses and also for other buildings, in particular prefabricated schools and the like.
In this connection, problems which are difficult to solve arose as a consequence of moisture deposition in the foundation, which gave rise to microbial growth, unpleasant smells and rot damage to the building.
The causes of these problems may be poor ground conditions combined with poorly executed foundation work. Other factors also have an effect, however, such as modern improved insulation materials which mean inter alia that thermal insulation of the floor structure is 5-6 times better compared with previously used sawdust-filled floor structures. Furthermore, there are not normally any heat-providing chimneys extending down into the crawl space.
In order to cope with damp and mildew problems, many different solutions have been proposed with a view to improving and/or regulating the ventilation of foundation crawl spaces. Attempts have even been made to keep them dry by making the foundations as heated foundations. In this connection, the foundations were sealed and thermally insulated and also ventilated by means of indoor air or specifically heated air from the heated part of the building. Such foundations are relatively expensive, and the technique can be difficult to apply in existing buildings. As the whole foundation is to be ventilated by indoor air, very large air volumes also have to be handled. An example is disclosed in SE-C-170061. The prior art also includes the mounting of separate drying equipment in the crawl-space foundation.
Proposals exist in which this technique is combined with a method for bringing about warm floors, see for example SE-B-8007770-4. In this case, warm indoor air is conducted in a gap between the inner floor and the floor structure insulation before it passes down into the insulated foundation and is then drawn out. This method is difficult to use in existing buildings and does not eliminate the requirement for complete sealing and insulation of the entire crawl space. The necessity of handling very large volumes of heated indoor air also remains.
Common to many of the methods proposed today for improving the ventilation of crawl-space foundations is the attempt to turn the whole of the free crawl space into a climate-controlled zone in one way or another. This entails inter alia the abovementioned problem of having to handle very large air volumes. Furthermore, the foundations are usually constructed only with a view to static bearing capacity, which means that the tightness is in most cases very poor. In the laying of foundation walls made of foundation blocks, the butt joints are often entirely unfilled. Complete sealing of the whole crawl-space foundation is very difficult and costly to effect.
It has previously been proposed to divide the crawl space into different zones. SE-B-7511197-1 describes the use of a perforated air-distributing layer. The upper and lower zones therefore communicate with one another via the layer. In order to push air down into the lower zone, a higher pressure is used in the upper zone, which also means that air can be pushed back up into the building. Leaks often occur at pipe bushings and other connections, which make it virtually impossible to prevent the positive pressure in the foundation pushing possibly bad air from the foundation up into the building. If radon gas is present, this too will be pushed up into the building.
SE-C2-507461 also describes a foundation with a horizontal partition. This partition is intended to cause the ventilation air, which has been taken in via outdoor air vents, to flow along the lower surface of the floor structure, then to be drawn down into the foundation and discharged to the outside of the building. For the ventilation described, it is necessary for the entire foundation to be placed under negative pressure, which requires complete sealing of the whole foundation. This is not only costly but also very difficult. With outdoor air vents of this type, major problems also arise as a consequence of the positive or negative pressure the wind pressure brings about on the different sides of the building. With the construction disclosed, it is likely that there is a positive pressure in the foundation at least at times. The fan must nevertheless be dimensioned to handle very large quantities of air on account of inevitable leaks of the foundation wall also.
As the known construction uses outdoor air, this readily leads to condensate being deposited both in distribution ducts and on the screening panel. Even if warm indoor air from the building were used instead of outdoor air, condensate would be deposited, especially during the winter, when warm air, which can contain more moisture per unit of volume than cold air, is drawn down into the cold foundation, where moisture would then be precipitated.
The basis of the present invention is constituted by the knowledge that, for successful ventilation of crawl-space foundations, it is necessary to limit the volume of the foundation where the ventilation is to be monitored and controlled. This results in smaller quantities of air having to be handled and sealing of only a limited space being necessary, which is relatively easy to achieve compared with sealing an entire crawl-space foundation.
According to the present invention, this is achieved by virtue of the fact that the crawl space is divided into upper and lower climate zones, which are sealed in relation to one another by means of a tight climate screen. In this connection, the upper climate zone is flowed through by warm indoor air, which keeps this climate zone dry and well ventilated, which prevents moisture deposition and mildew attack on, for example, the floor above the crawl space. No regulation of the environment in the lower climate zone is then required, this zone being ventilated in a conventional manner by means of outdoor air vents in the surrounding foundation walls.
The particularly characteristic feature of a method of the type indicated in the first paragraph is then, according to the present invention, that the crawl space is divided into at least one upper and at least one lower climate zone, that the two climate zones are separated from one another by means of an essentially windtight and vapourtight climate screen which forms a tight partition between the climate zones, that the climate screen is arranged at such a height in the crawl space that the outdoor air vents in the foundation walls communicate with only the lower climate zone, that the upper climate zone is provided with at least one supply air opening and at least one exhaust air opening, that the supply air opening is connected to a room above in the building and the exhaust air opening is connected to a discharge duct, and that a fan is arranged in association with the discharge duct so as to maintain a lower pressure in the upper climate zone than the pressure in said room above, so that the upper climate zone is ventilated by indoor air from the building and the lower climate zone is ventilated by outdoor air.
If this method is applied, a dry and well ventilated space is obtained on the underside of the floor above the crawl space, which eliminates the risk of moisture deposition and mildew formation. As the volume of this space is relatively limited, it can be sealed easily, so that an effective negative pressure can be maintained in this zone. This prevents bad air, radon gas or the like being drawn up into the building above. The requirement for sealing the whole crawl space is also eliminated.
If necessary, the supply air opening can be provided with a connecting duct for supplying dried air from a drying apparatus.
It is preferred that the climate screen is thermally insulated so as to avoid any appreciable cooling of the ventilation air passing through the upper climate zone.
Other characteristics of this method and of an arrangement for use in application of the method emerge from the subsequent patent claims.
The invention will be described in greater detail below with reference to the embodiments shown by way of example in the accompanying drawings.